Recently, vehicle makers have developed vehicles with enhanced fuel consumption as central tasks due to global high oil prices and regulations of carbon dioxide (CO2). The technological development of the enhancement of fuel consumption and environmentally-friendly vehicles includes a torque converter applied to an automatic transmission of the vehicle.
The torque converter of the automatic transmission includes an impeller directly receiving a rotation power of the engine, a turbine arranged opposite to the impeller and driven by a fluid supplied from the impeller, and a stator disposed inside facing parts of the impeller and the turbine and executing an operation of torque multiplication.
Also, a torque converter of the automatic transmission has a lock-up clutch capable of directly and mechanically transmitting the torque in a high speed range, and the lock-up clutch is disposed at a space formed between a front cover directly connected to the impeller as the rotation member of an input side of the torque converter and the turbine as the rotation member of an output side.
Also, as the lock-up clutch is operated in the high speed range except for an oscillation using the torque multiplication operation or a shift that is necessary to allow for a relative rotation of the impeller and the turbine, the fuel consumption performance may be improved.
However, since the general lock-up clutch allows the hydraulic pressure that is filled to transmit the power between the impeller and the turbine in the torque converter case to be supplied as an engage hydraulic pressure, the effective control may be obtained.
In more detail, to transmit the power between the impeller and the turbine, operation oil is filled in a case of the torque converter, however the hydraulic pressure in the case is largely changed depending on the rotation speed of the impeller, the rotation speed of the turbine, and the relative speed ration of the impeller and the turbine.
When the operation hydraulic pressure is acts upon the piston of the lock-up clutch as the engage hydraulic pressure, since the engage force acting on the lock-up clutch is changed, the engage and slip control of the lock-up clutch is not properly executed.
Also, to act as the engage hydraulic pressure of the lock-up clutch, since the operation hydraulic pressure must be actually applied with high pressure over the operation hydraulic pressure, a hydraulic pump of high-capacity is required, a power delivery efficiency of the transmission is resultantly deteriorated, and the fuel consumption performance is deteriorated due to the increasing of the engine load.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.